The present invention relates to a refractory plate unit and to a sliding closure unit assembly incorporating such refractory plate unit. More particularly, the present invention relates to such unit and assembly to be incorporated into a sliding closure unit or slide gate valve for controlling the discharge of molten metal from a discharge spout of a metallurgical vessel. Further particularly, the present invention is directed to such a unit and assembly wherein the refractory plate unit includes at least one metal band or member therearound and has therethrough at least one discharge opening. Still more particularly, the present invention relates to such a unit and assembly wherein the refractory plate unit is inserted loosely into a metal frame of the sliding closure unit assembly, i.e. without the need for positioning the refractory plate unit within the metal frame by means of clamping or locking mechanisms.
In known sliding closure units it has been conventional to mount a refractory plate or refractory plate unit in a metal frame by means of clamping or locking mechanisms. Such arrangement however has the disadvantage that removal and replacement of the refractory plate unit is a difficult and time consuming matter. This disadvantage is overcome in accordance with one known arrangement, disclosed in DE-OS 22 27 501, wherein a refractory plate unit is mounted within a metal frame without clamping or locking mechanisms, i.e. a so-called loose insertion or mounting. This known arrangement has the advantage that the refractory plates, that are subjected to very severe wear, can be removed and replaced in a more simple operation without the need for clamping tools. Additionally, this known arrangement has the further advantage that the loose insertion or mounting of the refractory plates prevents or substantially reduces, the formation of stress cracks in the plate that can occur due to thermal expansion when a refractory plate is firmly and fixedly clamped in position. However, this known arrangement suffers from certain inherent disadvantages. Thus, production of refractory plates inevitably requires production tolerances of up to several millimeters over the length and width of the refractory plates. This is due to firing of the plates as well as for other reasons that would be understood by one skilled in the art. For economical reasons it is not practical to machine the plates or to machine an entire metal shell often employed to surround the plates. Thus, there is the risk that the refractory plate unit, or a refractory plate unit and an accompanying refractory spout sleeve, will be inserted into the metal frame with several millimeters tolerance therebetween. Accordingly, when the refractory plate unit or the metal frame supporting the refractory plate unit is moved, there will occur relative movement therebetween. The refractory plate and the adjoining spout sleeve often are built as a unit, since when the sleeve is inserted separately mortar between the refractory plate and the sleeve can be destroyed due to such relative movement. Consequently, there exists the danger that the molten metal can break through such destroyed mortar. On the other hand, with regard to a stationary refractory plate and a stationary spout sleeve, the sleeve is rapidly worn and eroded during use. The stationary plate and stationary sleeve normally are joined by an interlocking depression and projection. However, when it becomes necessary to change the plates frequently, proper centering no longer can be achieved reliably. Therefore, the sleeve also must be frequently replaced despite the difficulty in such an operation.